Apparatuses of this kind, which are also referred to as punching/welding machines, are used as a preference in the manufacture of bumpers, produced from plastics material, for the automobile industry. The object in this case is for example to provide the bumpers with holes by punching in a first pass. After this, in a second pass, parts for receiving various additional items are to be inserted in these holes and fastened in place in them by welding or bonding. The additional items may for example be parking sensors, headlight cleaning systems, trailer hitches, exhaust systems or trim strips. As dictated by the particular case, the holes may comprise closed circular holes, or cutouts, open at the edge, of cross-sections which depend in each case on the particular application. The fastening of the receiving parts in the holes can be effected by ultrasonic or laser welding or the like or also by bonding.
Because of the two passes which belong together, it is usual to provide an apparatus of the kind referred to above and having combined therein punching and welding/bonding means. These are so designed that, with the shuttle table moved forward to a front end of the apparatus or machine, the bumpers are inserted manually into the holder mounted on the table, whereupon the shuttle table is moved, by a motor or the like, to a punching yoke which is arranged at the rear end of the apparatus, for the requisite holes first to be punched there. Following this, the shuttle table is moved back to the front end for the requisite receiving parts, which have previously been placed on delivery spigots arranged in the welding space, to be inserted into the holes which have been punched and then fastened in place in them.
Because of the manual insertion of the bumpers in the holder and of the receiving parts on spigots or the like intended for them on the holder, it is desirable for the holder to be arranged at an ergonomically advantageous height above the ground. In particular, the holder should not be arranged at too high a level, so that the operator does not have to lift the bumpers or other large workpieces to a position which can only be reached with inconvenience.
Something that militates against an ergonomically advantageous heightwise position of this kind for the holder is the fact that bumpers are in most cases parts of U-shaped cross-section which have to be inserted in the holder with the opening of the U facing downwards. Before the shuttle table can be moved to the punching station, the welding or bonding tools therefore have to be withdrawn downwards from the U-shaped space in the bumper inserted in the holder. After this, the shuttle table can be moved to the punching station. Because the shuttle table moves along a substantially horizontal path, the die in the punching yoke has to be situated in a lowered position when this happens so that the leading side-wall of the bumper, which forms the U-shape, can get past it. After this, the punching yoke has to be raised in order to apply the die to the underside of the bumper from below and thereby to support the bumper during the punching operation. Because in addition the punching axes are usually situated in radial positions relative to the arched surfaces of the bumper and the axes along which the punching yokes move are therefore situated at different angles in space, each punching yoke requires a reciprocating arrangement of its own to perform the movements described when there are a plurality of holes to be punched. The length of reciprocating travel has to be at least sufficiently great in this case as to be equal to the height of the side-walls of the bumpers, which means that sufficient space has to be left for it. After this, similar conditions arise at the front end of the apparatus at the welding/bonding station because there, all the tools required for welding or bonding likewise first have to be brought up against the bumpers from below and on completion of the welding or bonding operation have to be withdrawn again from the path of the bumpers.
As a result of these circumstances it has, to date, been necessary for the holders for the bumpers to be arranged at a certain minimum height which is not always the same as the height of insertion for the bumpers or receiving parts which is ergonomically most advantageous for the operator.